Peter wrote:
It may be “normal” but when I started flying IFR in 2005 I would regularly see temps like -15C to -25C in May or September, FL180, whereas in the last 2-3 years it has been 10C or more warmer.But surface temps have hardly changed.
I can not really comment on this as it has not been mentioned in any kind of updates we have seen. However, there are a multitude of reasons why this may happen. What is certainly true is that in recent years, we have had quite prolonged summers, some starting early and finishing late, as right now. This however is a cyclic thing, I remember the 1970ties where we had hot and long summers, then a period in the 1990ties and early 2000’s when Summers here hardly deserved the name. What happens right now is quite fine with me.
Surface temps have not changed per se but seasons have and they also have influenced the distribution of surface temperature. However, temps as we have them now in September with up to 28 degrees day temps are not abnormal at all, this period of late summer has different names in different places, but is well known. (Indian Summer being one more popular in the US). I quite enjoy the one we are having right now.
I think that if surface temps in say September were repeatedly 10C warmer, somebody would notice.
Peter wrote:
But surface temps have hardly changed.Do you measure surface temperature as keenly and with the same accuracy as you do altitude temperature though?
It may be “normal” but when I started flying IFR in 2005 I would regularly see temps like -15C to -25C in May or September, FL180, whereas in the last 2-3 years it has been 10C or more warmer.
But surface temps have hardly changed.
I’d call this normal summer temps. Remember flying at FL170 with the Mooney at an 0 degrees C OAT. Made 22’000 ft DA if I remember right.2011 if I am not mistaken.
As for the original question, not normally but not unheard of either. It can happen under different conditions, e.g. starting from a prefrontal cold air into a warm front or during inversion conditions or if wind direction changes with height.
Last week I flew from Monchengladbach to Siena and back. Both flights at FL140 @2-4 dC. However, temperature in Italy on the ground was 30 dC. Therefore 2dC is the natural result of 2C / 1000ft (2 × 14 = 28). Germany less so, but still not below 0.
Antonio wrote:
Yes it is getting warmer, I rarely fly at ISA at altitude nowadays
Absolutely! It’s feels like six months ago when I last flew at ISA … on sea level !
We call it summer!
Yes it is getting warmer, I rarely fly at ISA at altitude nowadays
Peter wrote:
I don’t think so. There are enough pilots on EuroGA who fly fairly high up. Maybe not flying as much in 2020 as on other years but still we could get some reports
I never had doubts that pilots can adequately report if / how often they see high temperatures in the levels today. But your question was not, how often you see it today but if it is more often than and or warmer than 10 years ago.
An no-one who did not do very accurate notes can remember today, how often they have seen ISA+12 (to use LFHNs example) 10 years ago. That’s pure “it feels like getting warmer” speculation.
Just to set a point against it: I actually “remember” that many decades ago, when I was a child", the summers have been much warmer than today: I remember many days we spend at the lokal lake w/o any rain. I remember strong sunburns. I remember clear skies and above 30 deg continuously for many weeks when I was 8 or so.
So to answer your question: Can’t say if atmosphere is getting warmer at high altitudes – but it is for sure getting colder and much more rainy at surface level in July/Aug – that’s at least what I remember and there are enough people here who could give you reports, that we had rain in July/Aug this year!
Peter wrote:
+3C at 12k is quite warm…
ISA+12. Equals 27C at seal level. Yes, that is quite warm – but also 10 years ago all but unusual for a warm summer day in southern France.
+3C at 12k is quite warm…
A topic like that can only be discussed based on hard data from flight instrument recordings.
I don’t think so. There are enough pilots on EuroGA who fly fairly high up. Maybe not flying as much in 2020 as on other years but still we could get some reports. Whether the many people will contribute is, of course, another question 
One previous thread on a similar topic is here. Flying in the summer is probably a part of the story.
